WO2011153126A2 - Concordance d'une référence étendue pour mesure de paramètres dans un système de détection optique - Google Patents

Concordance d'une référence étendue pour mesure de paramètres dans un système de détection optique Download PDF

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WO2011153126A2
WO2011153126A2 PCT/US2011/038512 US2011038512W WO2011153126A2 WO 2011153126 A2 WO2011153126 A2 WO 2011153126A2 US 2011038512 W US2011038512 W US 2011038512W WO 2011153126 A2 WO2011153126 A2 WO 2011153126A2
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pattern data
measurement
interferometric pattern
interferometric
shift
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PCT/US2011/038512
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WO2011153126A3 (fr
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Mark E. Froggatt
Justin W. Klein
Dawn K. Gifford
Matthew Reaves
Joseph J. Bos
Alexander K. Sang
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Luna Innovations Incorporated
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Priority to EP19163646.3A priority Critical patent/EP3581878B1/fr
Priority to EP11790271.8A priority patent/EP2577222B1/fr
Publication of WO2011153126A2 publication Critical patent/WO2011153126A2/fr
Publication of WO2011153126A3 publication Critical patent/WO2011153126A3/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02083—Interferometers characterised by particular signal processing and presentation
    • G01B9/02088—Matching signals with a database
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02023—Indirect probing of object, e.g. via influence on cavity or fibre
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02062—Active error reduction, i.e. varying with time
    • G01B9/02067—Active error reduction, i.e. varying with time by electronic control systems, i.e. using feedback acting on optics or light
    • G01B9/02069—Synchronization of light source or manipulator and detector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02083—Interferometers characterised by particular signal processing and presentation
    • G01B9/02084—Processing in the Fourier or frequency domain when not imaged in the frequency domain
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
    • G01D5/35354—Sensor working in reflection
    • G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
    • G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means

Definitions

  • the technology relates to interferometric measurements and applications thereof.
  • Optical strain sensing is a technology useful for measuring physical deformation of a waveguide caused by, for example, the change in tension, compression, or temperature of an optical fiber.
  • Optical fiber strain sensing with fiber Bragg gratings uses a spectral shift induced by a strain on the fiber as a basic measurement technique. The shift in the Bragg spectrum is a result of the elongation or compression of the period of the periodic modulation of index that forms the Bragg grating. Strain is thus encoded onto wavelength and read out using a spectrometer. Froggatt and Moore, "High spatial resolution distributed strain measurement in optical fiber using Rayleigh scatter," Applied Optics. April 1 , 1998, and U.S.
  • v c represents the center frequency of the measurement spectral range, i.e., the range of optical frequencies that the light source was swept through during a measurement scan.
  • the fiber with Bragg gratings is shifted such that the signal is outside the measurement spectral range, and as a result, this particular measurement does not detect any signal.
  • Rayleigh scatter in the upper right graph a signal is detected across the entire measurement spectral range.
  • the baseline Rayleigh scatter pattern, in the upper left graph is preserved but shifted as a result of strain, and the measurement captures a segment of this shifted pattern.
  • the ability to measure a shifted version of the baseline Rayleigh scatter pattern regardless of applied strain offers an advantage over Bragg grating-based sensing techniques.
  • a cross- correlation may be used to determine a shift between the reflected spectrums of a baseline and strained measurement.
  • the measured shift required to match the reflected spectrums can be directly scaled to a measure of strain.
  • straining the waveguide reduces the commonality or correspondence between a reference pattern and a measurement pattern as points are shifted out of the spectral range of the measurement. As more uncommon points are compared, a reduction in the strength of the measured correlation is observed.
  • Rayleigh scatter is generally a weak (low level) signal
  • the quality of a cross-correlation, the amplitude of the correlation peak
  • a strain can be applied that entirely shifts all common points with a reference Rayleigh scatter pattern beyond the spectral range of the measurement rendering a cross- correlation approach ineffective.
  • optical strain sensing technology that preferably enables sensing of high strains, maintains sufficient signal-to-noise levels in the presence of small strains, and achieves physical alignment without knowledge of the strain state of the sensing waveguide leading up to a measurement segment.
  • One example embodiment describes an interferometric measurement system for measuring a parameter using at least one optical waveguide.
  • optical waveguides include silica-based optical fiber, polymer-based optical fiber, and photonic integrated circuits.
  • a memory stores reference interferometric pattern data associated with a segment of the optical waveguide.
  • Interferometric detection circuitry detects and stores measurement interferometric pattern data associated with the segment of the optical waveguide during a measurement operation.
  • a spectral range of the reference interferometric pattern of the optical waveguide is greater than a spectral range of the measurement interferometric pattern of the optical waveguide.
  • Processing circuitry shifts one or both of the measurement interferometric pattern data and the reference interferometric pattern data relative to the other to obtain a match. The shift value at which a match is observed is then used to measure the parameter.
  • the apparatus corresponds to an optical strain sensing system configured to use Optical Frequency Domain
  • OFDR 5 Reflectometry
  • o processing circuitry compares a subsequent OFDR measurement of scatter pattern data in the spectral and/or temporal domains relative to the other to obtain a match.
  • the shift value at which a match is observed is then scaled to measure the parameter.
  • the interferometric pattern data corresponds to a Rayleigh scatter pattern in the optical waveguide
  • the parameter corresponds to
  • the processing circuitry determines a spectral shift in the spectral domain of the Rayleigh scatter in the optical waveguide segment to measure the strain.
  • a temporal shift in the temporal domain of the Rayleigh scatter in the optical waveguide is determined in order to measure change in length of the waveguide.
  • the reference segment data extends further in the spectral domain and the temporal domain than the measurement segment data.
  • the shift of one or both of the measurement interferometric pattern data and the reference interferometric pattern data in the spectral domain allows a match to
  • the measurement interferometric pattern 25 be detected even if the measurement interferometric pattern is shifted beyond a spectral range of measurement associated with the measurement operation.
  • the shift of one or both of the measurement interferometric pattern data and the reference interferometric pattern data in the temporal domain allows a match to be detected even if the
  • a search algorithm which searches for a match of the measurement interferometric pattern data within the reference interferometric pattern data to achieve spectral and/or temporal registration between them.
  • a match may be an exact match, a closest match, or a matching value that exceeds a predetermined matching threshold
  • a processor determines a spectral and/or temporal shift for the match, and that determined spectral shift and/or temporal shift corresponds in one application to a strain applied to the segment.
  • the processor incrementally shifts one or both of the measurement interferometric pattern data or the reference interferometric pattern data and compares the shifted measurement interferometric pattern data against the reference interferometric pattern data at each shift to produce a correlation quality value between the reference interferometric pattern data and the measurement interferometric pattern data.
  • Pattern data registration may be performed, for example, by
  • the processing circuitry multiplies the measurement interferometric pattern data or the reference interferometric pattern data by a phase slope in the temporal domain to shift the measurement interferometric pattern data or the reference interferometric pattern data in the spectral domain and multiplies the measurement interferometric pattern data or the reference interferometric pattern data by a phase slope in the spectral domain to shift the measurement interferometric pattern data or the reference interferometric pattern data in the temporal domain.
  • the quality factor increases when an average difference between the reference interferometric pattern data and the measurement interferometric pattern data moves closer to zero.
  • the processing circuitry selects a temporal shift and a spectral shift combination that produces a correlation associated with a highest quality factor.
  • the technology in this application also permits a reduction in the spectral range of the measurement segment to enable sensing of the parameter at a length along the optical waveguide on the order of or greater than 100 meters.
  • Another application of this technology uses the extended spectral range of the reference pattern data to prevent a reduction in signal-to-noise ratio that would otherwise occur when the measurement interferometric pattern data is shifted partially or beyond a spectral range of measurement for the segment.
  • Yet another application of this technology uses the technique of OFDR to produce a continuous measure of strain along a length of a waveguide.
  • strain scatters are physically shifted, and the respective OFDR measurement scatter pattern data signals are delayed in the temporal domain.
  • a measured shift in delay corresponds to a continuous, slowly varying optical phase signal when compared against the reference scatter pattern data.
  • the processing circuitry determines a derivative of the optical phase signal which corresponds to a change in physical length of the segment of the optical waveguide.
  • the processing circuitry scales the change in physical length to produce a continuous measurement of strain along the optical waveguide.
  • the technology further includes an interferometric measurement method for measuring a parameter associated with at least one optical waveguide:
  • a spectral range of the reference interferometric pattern of the optical waveguide is greater than a spectral range of the measurement interferometric pattern of the optical waveguide
  • Another aspect of the technology is a non-transitory, computer-readable storage medium for use in an inter ferometric measurement system having an optical waveguide.
  • the non-transitory, computer-readable storage medium stores a computer program comprising instructions that cause a computer-based OFDR system to perform the following tasks:
  • Figure 1 shows graphs of examples of unstrained and strained Rayleigh scatter interferometric signals and unstrained and strained Bragg grating interferometric signals
  • Figure 2 shows graphs of examples of unstrained (reference) and strained
  • FIG. 3 is a graph showing an example of a shifted (measurement) and unshifted (reference) version of a continuous scatter pattern
  • Figure 4 is a graph showing an example of truncated versions of the shifted measurement pattern and the unshifted reference pattern
  • Figure 5 is a graph showing an example of aligned reference and measurement scatter patterns depicting a reduced overlap region
  • Figure 6 is a graph showing an example of a reference scatter pattern with a spectral range greater than the spectral range of a measurement scatter pattern
  • Figure 7 is a graph showing an extended reference example where a measurement scatter pattern can be matched to a reference scatter pattern even in the case when the measurement scatter pattern is shifted because of a large strain beyond the spectral range of the measurement;
  • Figure 8 shows an example where as an optical fiber is strained, a physical segment of fiber is shifted as the fiber is physically longer;
  • Figure 9 is a non-limiting example of an OFDR-based fiber optic sensing system
  • Figure 10 shows example graphs that illustrate how a linear phase slope applied in one domain induces a shift in the transform domain
  • Figure 1 1 is a flowchart of a non-limiting example procedure that searches for a quality of correlation over a range of temporal and spectral shifts;
  • Figure 12 shows a non-limiting, example of a grid plot representing quality of correlation over a range of spectral and temporal shifts applied to a reference data set
  • Figure 13 shows a non-limiting, example comparing the real component of complex reference scatter pattern data and of measurement scatter pattern data in the spectral domain
  • Figure 14 shows a non-limiting, example comparing the imaginary component of complex reference scatter pattern data and of measurement scatter pattern data in the spectral domain
  • Figure 15 is a non-limiting example test configuration
  • Figure 16 is a graph showing an example of temporal displacement due to the increase in physical length of the optical fiber
  • Figure 17 is an example of strain produced from a spectral shift search procedure
  • Figure 18 shows an example strain measurement setup for a long range strain sensing system
  • Figure 1 is a graph showing an example of strain-induced wavelength shift calculated using both extended reference and standard reference for an example 1 .5 kilometer strain sensing application;
  • Figure 20 is a graph showing an example of distributed strain profiles of a helically spun shape sensing fiber with a 25mm loop, 15mm loop, and a 10mm loop as determined using a registration algorithm executed every 1.28 millimeters:
  • Figure 21 is a graph showing an example of a phase difference found by extracting the argument from the product of the complex conjugate of the reference and measurement signals in the temporal domain;
  • Figure 22 is a function block diagram showing a non-limiting, example of optical phase tracking with an extended reference
  • Figure 23 is a graph illustrating how previous phase values may be used to estimate a required spectral shift for a next iteration.
  • Figure 24 is a graph illustrating the phase of a negatively, optical frequency-shifted set of reference and measurement data as compared to a phase of a positively, optical frequency-shifted set in the temporal domain to provide a measure of temporal delay between the reference and measurement data sets.
  • the functional blocks may include or encompass, without limitation, a digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)). and (where appropriate) state machines capable of performing such functions.
  • DSP digital signal processor
  • ASIC application specific integrated circuit
  • FPGA field programmable gate array
  • a computer in terms of computer implementation, is generally understood to comprise one or more processors or one or more controllers, and the terms computer, processor, and controller may be employed interchangeably.
  • the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed.
  • processor or “controller” also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.
  • the inventors overcame the problems identified in the background by recognizing that a reference interferometric pattern of an optical waveguide can be recorded over an extended spectral range, a range greater in optical frequency than that of a given interferometric measurement. Further, the reference interferometric pattern can be recorded to represent a larger length of the waveguide to accommodate physical displacement of the measurement segment as a result of strain. Limitations that prevent the proper measurement of higher strains on optical fibers are overcome by utilizing an extended reference interferometric pattern.
  • strain sensing technology gains valuable flexibility as it is no longer limited to a defined measurement scan range.
  • the figure contains a shifted (thin line) and an un-shifted (thick line) version of the same continuous Rayleigh scatter pattern.
  • These two scatter patterns represent an example reference scatter data set and strained measurement scatter data set in which the spectral index on the horizontal axis represents an increment of optical frequency,
  • a shift in spectral index may be determined that aligns the measurement with a portion of the reference pattern.
  • This shift in spectral index is proportional to a shift in optical frequency. Accordingly, determining the spectral shift required to find a pattern match within the reference pattern corresponds to determining the strain applied to the measured fiber.
  • the act of searching for a match within a reference pattern is referred to as spectral registration.
  • a match may include an exact match, a closest match, a match that exceeds some threshold, or other suitable matching criterion/criteria.
  • the optical frequency response of the fiber during a measurement is searched against a reference pattern with a greater spectral range then the measurement until the patterns are registered or in alignment in accordance with suitable matching criterion/criteria.
  • One example method is described as to how the measurement may be incrementally shifted and compared against the reference pattern at each shift to produce a measure of quality of correlation between the two data sets. Extending the spectral range in the reference pattern and quantifying alignment between the reference pattern data and measurement pattern data over a range of possible shifts provides an increased strain range for fiber optic shape sensing and a more robust strain sensing system than by using the measurement scan range alone. Further, with the maximum detectable strain being decoupled from the measurements spectral range, low cost-high speed systems can be designed that perform smaller wavelength scans reducing data size and light source requirements, such as tuning range.
  • a robust strain sensing system preferably obtains registration in physical distance without knowledge of the strain state of the waveguide leading up to the measurement segment.
  • a robust strain sensing system also preferably correlates reflected spectrums in the presence of high strain and detects physical displacement of a measurement segment of fiber due to expansion/compression of the fiber preceding the measurement segment.
  • the concept of a reference extended in spectral range allowing correlation to be maintained when a reflected spectrum is shifted out of the spectral range of the measurement may be adapted to extend the reference in physical distance to accommodate physical displacement of a measurement segment.
  • FIG. 9 illustrates a non-limiting example of an OFDR-based distributed strain sensing system.
  • a system controller 10 initiates a tunable light source 12, e.g., a tunable laser, to scan through a range of optical frequencies.
  • Light enters the sensing or measurement fiber 18 through a measurement path of an interferometric interrogator 16,
  • An interferometric interrogator 16 includes an optical circulator coupling the measurement fiber 18 to an input optical coupler and output optical coupler.
  • a reference path extends between the input optical coupler and output optical coupler. Light scattered from the sensing fiber interferes with light that has traveled through the reference path.
  • a laser monitor network 14 provides an absolute
  • the laser monitor network 14 uses an interferometer to measure tuning rate variations throughout the scan.
  • Data acquisition electronic circuitry 20 includes optical detectors, e.g., photodiodes, to convert measured optical signals to electrical signals.
  • the system controller data processor 10 resamples the interference pattern from the measurement fiber using the laser monitor 14 outputs, also converted to electrical signals by corresponding optical detectors, to ensure the data are sampled with a constant increment of optical frequency. This resampling is required for the Fourier transform operation.
  • the system controller data processor 10 Fourier transforms the resampled sensing fiber signal to the temporal (time) domain and produces a complex signal of scatter amplitude and phase versus delay along the measurement fiber length. Using the distance light travels in a given increment of time based on the known speed of light, the delay may be converted to a measure of length along the sensing fiber.
  • the scatter signal depicts each scattering event as a function of distance along the fiber.
  • the sampling period is referred to as the spatial resolution and is inversely proportional to the frequency range that the tunable light source is swept through during the measurement.
  • the local "scatters" shift as the fiber changes in physical length. It can be shown that these strain-induced distortions are highly repeatable.
  • the OFDR measurement signal describes the physical locations of the scattering events. Applying an inverse Fourier transform to that signal produces a measurement signal in the spectral domain that describes the optical frequency response of the fiber. Using the information from both transform domains allows measurement of a strain response by correlating the reflected spectrum with a reference pattern in the spectral domain and also allows measurement of physical displacement by correlating the scatter pattern with a reference pattern in the temporal domain.
  • the quality of the cross-corre!ation begins to degrade as points are shifted beyond the spectral range of a given measurement and as points are shifted beyond the physical range of the measurement.
  • This example embodiment of OFDR strain sensing system overcomes this degradation by maintaining measurement registration in both the spectral and temporal domains.
  • An extended reference enables one to maintain registration over a wider range of strain and/or displacements.
  • registration may be performed by systematically shifting a given measurement or reference in both the spectral and temporal domain and evaluating the quality of the correlation at each combination.
  • a shift applied in either the temporal or spectral domain may be mathematically implemented by utilizing a property of the Fourier transform.
  • Delay in the frequency domain is a linear phase term in the time domain as depicted by Eq. 1 , Eq. 2, and Eq. 3 in which t represents time and ⁇ represents frequency.
  • delay in the time domain is a linear phase term in the frequency domain as shown with Eq. 4, Eq. 5, and
  • a temporal shift and a spectral shift may be applied to the reference data and then compared to the measurement signal.
  • a temporal shift and a spectral shift may be determined that result in a high quality correlation.
  • the spectral shift is preferably equal to the optical frequency shift induced by the strain on the measurement and the displacement of the measurement segment in physical distance can be scaled from the found temporal shift.
  • Segments in the reference and measurement data are selected, where the reference segment is larger than the measurement segment in both the temporal and spectra! domains (step S I 00).
  • a 40 nanometer reference scan and a 5 nanometer measurement scan were selected.
  • the reference segment is preferably sufficiently large to accommodate expected temporal shifts from the applied strain. For example, 1000 microstrain of tension applied over 1 meter of fiber leads to a 1 mm temporal shift by the end of the strained region.
  • the reference segment is preferably at least 1 mm longer on each side than the measurement segment to allow for the desired data registration in this example.
  • One spectral index shift is induced by multiplying the reference segment in the time domain by a phase slope that runs between - ⁇ and -He.
  • the temporal reference segment is longer than the measurement segment, but the slope is calculated to run between - ⁇ and + ⁇ over the length equivalent to the length of the measurement segment. For example, if the measurement segment represents a 2 mm region in the fiber, and a reference segment 4 times longer than the measurement length is used to account for temporal shifts, the reference segment is 8 mm long.
  • the phase slope in the time domain is calculated such that it runs from - ⁇ to + ⁇ over the 2 mm in the center of the data to induce a single index spectral shift. This avoids changing the applied spectral shift when the reference segment length is changed.
  • the data is then transformed into the spectral domain using an FFT (step S I 03 ) and then truncated in the spectral domain such that the reference data covers the same spectral range as the measurement data (step S I 06).
  • the reference data might be truncated to 1/16 of its original size in the center of the data.
  • the reference data is still larger than the measurement data by the amount of extra points selected in the temporal domain.
  • One temporal index shift is induced by multiplying the reference data by a phase slope running between - ⁇ and + ⁇ in the spectral domain over the remaining data size (step S I 08). There is no need to adjust for extra points as the data has been truncated to the same spectral range as the measurement data.
  • step S 1 The resulting data is then transformed back to the temporal domain using an inverse Fourier transform (step S 1 10) and then truncated in the center of the time domain to the same length as the measurement segment (step S I 12).
  • step S 1 The two data sets are now equal in length in both the temporal and spectral domains and have the same number of points.
  • step S I 12 The next step is to evaluate how closely the reference and
  • a correction factor can then be assembled with these two quantities and applied to the reference data as seen in Eq. 9.
  • the overlap quality factor increases when the average difference between the complex reference data and the measurement data set moves closer to zero. This subtraction of complex numbers is one way to evaluate the similarity of both the real and imaginary components.
  • the flowchart in Figure 1 1 may be used to produce a lookup table in which a range of temporal shifts are crossed with a range of spectral shifts. By selecting the temporal and spectral shift combination that produces the highest quality factor, (step S I 16), the induced temporal and spectral shifts imposed on that particular measurement segment when compared with the reference data may be determined. This routine in Figure 1 1 may be run along the length of a fiber to determine a measure of both strain verses length (spectral shift) and change in length of the waveguide (temporal shift).
  • Figure 12 depicts an example of the overlap quality factor calculation over a grid of spectral and temporal shifts.
  • the gray scale indicates how well the reference and measurement match, with black being a high quality factor. Black indicates a strong correlation while white represents a weak correlation strength,
  • the degree to which the reference scatter pattern and measurement scatter pattern match may be determined based on a similarity between the real and and imaginary components of these complex scatter patterns, in Figures 13 and 14, the real and imaginary components, respectively, of the reference scatter pattern data and measurement scatter pattern data are compared in the spectral domain to illustrate the simularity in the data when the spectral and temporal shifts are applied to the reference scatter pattern data corresponding to the highest quality con-elation.
  • the algorithm outlined in Figure 1 1 may be stepped along the length of strained optical fiber to measure both temporal shift and spectral shift verses distance along the length of the fiber. Both quantities may be scaled to a measure of strain along the length of the fiber offering a robust algorithm for strain sensing.
  • a reference pattern for an optical fiber was recorded in an unstrained state using an OFDR based acquisition system for a spectral range of 40 nanometers.
  • the optical fiber was then axially strained using a setup depicted in Figure 15.
  • the axial load applied to the fiber was increased to a strain of 6000 microstrain.
  • a measurement was recorded with a spectral range of 5 nanometers.
  • Six thousand microstrain induces a wavelength shift of approximately 7.2 nanometers at a center wavelength of 1540 nanometers in standard SMF28 optical fiber.
  • the spectrum of the measurement is expected to be shifted beyond the 5 nanometer spectral range of the measurement.
  • Conventional cross-correlation approaches using a reference and measurement pattern matched in with a spectral range of 5nm are ineffective in this situation because all data points are shifted out of the spectral range of the measurement and no common points exist between the two datasets.
  • Axial strain is illustrated in Figure 17 and was calculated by scaling the spectral shift found along the length of the optical fiber using the registration algorithm, As expected, the strain is evenly distributed along the length of the optical fiber between the attachment points of the apparatus and quickly falls to zero strain after
  • the 40 nanometer reference pattern enabled a measurement of both temporal displacement and spectral shift along the length of the highly-strained fiber.
  • the applied strain was sufficient to induce a spectral shift that fully displaced the measurement outside of its spectral range. Further a substantial physical deformation i s of over 3 millimeters was induced over the 700 millimeter length of fiber, This
  • the results are summarized in Figure 19.
  • the dotted gray curve shows strain calculations performed through a standard-reference method, using a 0.807 nanometer scan range for both the reference and measurement patterns.
  • the standard- reference calculations break down around 0.5 nanometer wavelength shift as evidenced by the discontinuity of this line.
  • the black solid curve depicts strain calculated using a 21 , 18 nanometer extended reference and maintains continuity far beyond the strain values tolerated with a standard reference. Further, the extended reference enables wavelength shifts that exceed the spectral range of the measurement scan, 0.807 nanometers.
  • the extended reference-registration approach described above may also be used to provide more robust measurements of distributed strain than allowed by conventional cross-correlation approaches.
  • the cross-correlation signal is blurred as the period of the scatters is not constant.
  • the size of the measurement segment might be decreased, cross-correlations are not effective operating on small sets of data.
  • a shape sensing fiber can be constructed with independent optical cores that are helically spun along the length of the sensing fiber. Hence, when placed into a bend in a single plane, an outer core experiences periods of elongation and compression as it wraps about the shape sensing fibers central axis throughout the region of the bend.
  • the registration algorithm may be executed along the length of the fiber to produce a measure of strain along the length of the fiber, this does not produce a continuous measure of strain along the length of the sensing fiber because the algorithm is advanced in a stepped fashion. Even though the spatial resolution of the measurements may be increased by decreasing the step size, this becomes computationally expensive and does not ultimately produce a continuous measure of strain. In many distributed strain sensing applications, such as fiber optic position sensing, it is desirable to have a continuous measurement of strain to a high spatial resolution ( ⁇ 50um). Optical phase tracking is a powerful option for distributed strain sensing which provides a high spatial resolution and, by the nature of the measurement, a continuous measure of strain.
  • the OFDR technique may be adapted to produce continuous measures of strain as a function of distance by adopting optical phase tracking as described in commonly-owned, U.S. patent application 12/874,901 , filed on Sept 2, 2010, entitled “Optical Position and/or Shape Sensing,” incorporated herein by reference.
  • Figure 9 performing an OFDR measurement provides a measure of scatter amplitude verse fiber distance. As the structure of an optic fiber is distorted by strain, the amplitudes of individual scattering events that comprise Rayleigh scatter are preserved. In other words, the scatter profile of the fiber can only be compressed or elongated.
  • optical phase is a continuous signal along the length of the fiber, phase change can be tracked continuously with the full spatial resolution of the measurement. This change in optical phase is directly proportional to the accumulated change in length. A derivative of this optical phase signal can be directly scaled to a continuous measure of strain.
  • Optical phase tracking has similar limitations to that of the cross- correlation approach and these limitations can be overcome through the use of the extended reference and the registration technology described above. Namely, the highest phase change that can be tracked is defined by the spectral range of the measurement.
  • An extended reference allows extraction of a measure of phase change for a signal shifted beyond the spectral range of the measurement, thereby increasing the strain ranges that can be measured with the optical phase tracking technique.
  • OFDR data is complex-valued.
  • a measure of phase may be extracted by conjugating the reference data and multiplying against the complex valued
  • Figure 22 is a non-limiting example function block diagram of an optical phase tracking system that uses the concept of maintaining registration in the temporal and spectral domains to increase the robustness of the phase tracking algorithm. Furthermore, the extended reference concept is also applied to increase the strain range that can be measured with the technique of optical phase tracking.
  • the OFDR system is similar to that illustrated in Figure 9. However, the system controller/ processor 10 (or some other processor) performs the processing illustrated in block 22 and described below.
  • Reference data (A) in the temporal domain is retained in system memory (not shown) that is both longer in the temporal and spectral domains.
  • Measurement data (B) in the temporal domain is processed to select a segment or window of data.
  • the data segment window is advanced point by point (C) along the length of the fiber.
  • the reference data in the temporal domain is Fourier (FFT) transformed (D) into the spectral domain and then indexed (E) such that it is aligned with the measurement data in the spectral domain.
  • the reference data is then truncated (F) in the spectral domain such that it covers the same optical frequency range as the measurement data.
  • An inverse Fourier transform (G) is performed on the truncated reference data in the spectral domain to return the data to the temporal domain.
  • the reference data in the temporal domain is then indexed (H) so that it is temporally registered with the measurement data.
  • the registered reference data in the temporal domain is then truncated (1) such that its temporal range matches that of the measurement segment.
  • the reference and measurement segments are now equal in data size.
  • the reference data segment and measurement data segment are then compared to assess how well they are temporally aligned (J).
  • the output of this module is used as feedback (K) for the registration of the reference in the temporal domain as the registration algorithm is executed along the length of the fiber.
  • a complex multiply is performed between the complex conjugate of the reference scatter pattern and the complex measurement scatter pattern, and the points of the data segment are averaged (L).
  • a measure of optical phase is accumulated by extracting the angle of the averaged value (L) and summing the value with the previous optical phase value (M).
  • the optical phase signal may be used to produce an approximation of the shift in optical frequency as a result of strain in the measurement segment (N). This quantity can be used as feedback to register the reference and measurement data in the spectral domain (0).
  • the derivative of the optical phase signal will be proportional to the change in length between the measurement and reference scatter patterns along the length of the sensing fiber (P). This signal can be scaled to a continuous measure of strain along the length of the fiber (Q).
  • the algorithm is then advanced along the length of the fiber incrementally (R) using the feedback values determined in the previous iteration (K, O) to maintain registration between the reference and the measurement data in the temporal and spectral domains.
  • Temporal registration may also be maintained with a simple mathematical operation that does not require searching a wide range of temporal shifts.
  • a shift may be induced in one domain by adding a linear phase slope in the transform domain.
  • a phase slope is achieved in one domain by inducing a shift in the transform domain.
  • This shift may be implemented by any of several means.
  • the reference and measurement data may be shifted in the spectral domain by multiplying the data sets by a positively rotating complex number and then low pass filtering the dataset. When the reference and measurement are compared in the temporal domain, a slope will have been induced on the phase of the data sets.
  • the original reference and measurement data sets may then be multiplied by a negatively rotating complex number and low pass filtering the datasets. Again, when compared in the temporal domain, the data sets will have an induced phase slope, but this slope will be opposite in sign. Plotting both phase slopes produces a signed indicator of the temporal delay between the two data sets as illustrated in Figure 24.
  • phase of a negatively-shifted (in optical frequency) reference and measurement data set pair is compared to a phase of a positively-shifted reference and measurement data set pair in the temporal domain to provide a measure of temporal delay between the re erence and measurement data sets.
  • phase of the negatively-shifted (gray) (i.e., shifted in optical frequency) set of reference and measurement pattern data is opposite in slope when compared to the positively-shifted (black) set of reference and
  • Delay (a temporal shift) can be scaled, as explained above, to a distance along the length of the fiber by using the distance light travels in a given increment of time.
  • the black curve leads the gray curve before this crossing point, and the gray curve leads the black after this crossing point.
  • a signed indicator of temporal delay (either positive or negative) is obtained. This operation may be executed to measure the required temporal shift between two data sets for registration.
  • the extended reference allows use of lower cost light sources in the manufacture of strain sensing systems (laser cost is proportional to functional optical frequency tuning range of the light source).
  • the extended reference technology also enables sensing at greater distances along the length of a fiber while maintaining the ability to measure high strains.
  • the technology also may be applied to other structures, e.g., optical waveguides in an optical chip, free-space optical beams probing the same object, etc.
  • OFDR measurement is described in terms of Rayleigh scatter pattern data, Bragg grating inter ferometric data may also be used.

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Abstract

L'invention concerne un système de mesure interférométrique qui permet de mesurer un paramètre au moyen d'au moins un guide d'ondes optiques. Une mémoire enregistre des données de diagramme interférométrique de référence associées à un segment du guide d'ondes optiques. Des circuits de détection interférométrique détectent et enregistrent des données de diagramme interférométrique de mesure associées au segment du guide d'ondes optiques au cours d'une mesure. Une plage spectrale de diagramme interférométrique de référence du guide d'ondes optiques est supérieure à une plage spectrale du diagramme interférométrique de mesure du guide d'ondes optiques. Un processeur décale soit les données de diagramme interférométrique de mesure, soit les données de diagramme interférométrique de référence, ou les deux, les unes par rapport aux autres, pour obtenir une concordance et pour utiliser cette concordance afin de mesurer le paramètre. Une déformation est un exemple de paramètre.
PCT/US2011/038512 2010-06-01 2011-05-31 Concordance d'une référence étendue pour mesure de paramètres dans un système de détection optique WO2011153126A2 (fr)

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CN103968864A (zh) * 2014-04-23 2014-08-06 南京大学 用于准确测量布里渊谱的频移的最大相似匹配分析方法
WO2014153325A1 (fr) * 2013-03-19 2014-09-25 Intuitive Surgical Operations Inc. Procédés et appareil destinés à des mesures simultanées de paramètres optiques
EP2936048A4 (fr) * 2012-12-24 2016-08-03 Intuitive Surgical Operations Correction de dispersion dans une réflectométrie de domaine de fréquence optique (ofdr)
CN108344432A (zh) * 2018-02-07 2018-07-31 北京交通大学 获取布里渊光纤分布式传感系统的传感信息的方法
CN111856642A (zh) * 2016-05-11 2020-10-30 直观外科手术操作公司 具有用于安全性的冗余纤芯的多纤芯光学纤维
CN111854811A (zh) * 2015-04-02 2020-10-30 直观外科手术操作公司 使用参考光纤干涉数据配准测量的光纤干涉数据
US11125648B2 (en) 2019-06-07 2021-09-21 Exfo Inc. Duplicate OTDR measurement detection
US11478307B2 (en) 2018-12-18 2022-10-25 Mako Surgical Corp. Systems and methods for fiber optic tracking
US11650128B2 (en) 2020-06-30 2023-05-16 Exfo Inc. Optical fiber recognition using backscattering pattern
US11879802B2 (en) 2020-10-22 2024-01-23 Exfo Inc. Testing optical fiber link continuity using OTDR backscattering patterns

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US10545070B2 (en) 2012-12-24 2020-01-28 Intuitive Surgical Operations, Inc. Dispersion correction in optical frequency-domain reflectometry
EP2936048A4 (fr) * 2012-12-24 2016-08-03 Intuitive Surgical Operations Correction de dispersion dans une réflectométrie de domaine de fréquence optique (ofdr)
US9885633B2 (en) 2012-12-24 2018-02-06 Intuitive Surgical Operations, Inc. Dispersion correction in optical frequency-domain reflectometry
WO2014153325A1 (fr) * 2013-03-19 2014-09-25 Intuitive Surgical Operations Inc. Procédés et appareil destinés à des mesures simultanées de paramètres optiques
CN103438798A (zh) * 2013-08-27 2013-12-11 北京航空航天大学 主动双目视觉系统全局标定方法
CN103968864A (zh) * 2014-04-23 2014-08-06 南京大学 用于准确测量布里渊谱的频移的最大相似匹配分析方法
CN111854811A (zh) * 2015-04-02 2020-10-30 直观外科手术操作公司 使用参考光纤干涉数据配准测量的光纤干涉数据
CN111856642A (zh) * 2016-05-11 2020-10-30 直观外科手术操作公司 具有用于安全性的冗余纤芯的多纤芯光学纤维
US11624870B2 (en) 2016-05-11 2023-04-11 Intuitive Surgical Operations, Inc. Redundant core in multicore optical fiber for safety
CN111856642B (zh) * 2016-05-11 2023-04-25 直观外科手术操作公司 具有用于安全性的冗余纤芯的多纤芯光学纤维
CN108344432A (zh) * 2018-02-07 2018-07-31 北京交通大学 获取布里渊光纤分布式传感系统的传感信息的方法
US11478307B2 (en) 2018-12-18 2022-10-25 Mako Surgical Corp. Systems and methods for fiber optic tracking
US11819294B2 (en) 2018-12-18 2023-11-21 Mako Surgical Corp. Systems and methods for fiber optic tracking
US11125648B2 (en) 2019-06-07 2021-09-21 Exfo Inc. Duplicate OTDR measurement detection
US11650128B2 (en) 2020-06-30 2023-05-16 Exfo Inc. Optical fiber recognition using backscattering pattern
US11879802B2 (en) 2020-10-22 2024-01-23 Exfo Inc. Testing optical fiber link continuity using OTDR backscattering patterns

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EP2577222A4 (fr) 2017-06-28
WO2011153126A3 (fr) 2012-04-05

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